The present invention relates to a color cathode-ray tube, and relates, more particularly, to a color cathode-ray tube with an increased holding strength of a curved surface of a shadow mask to reduce deviation of beam landing.
In general, a color cathode-ray tube has a vacuum envelope which includes a substantially rectangular panel having an effective portion formed of a curved surface and a skirt portion provided on the periphery of the effective portion, and a funnel connected to the skirt portion. On the inner surface of the effective portion of the panel is formed a phosphor screen consisting of black non-light emitting substance layers and three-color phosphor layers buried in gap of the black non-light emitting substance layers. Inside the panel is disposed a substantially rectangular shadow mask facing the phosphor screen. Within a neck of the funnel is disposed an electron gun for emitting three electron beams. Inside a large diameter portion of the funnel, there is disposed an inner shield fitted to a mask frame of the shadow mask.
In the color cathode-ray tube, three electron beams emitted from the electron gun are deflected by a magnetic field generated from a deflector mounted on the outside of the funnel, and scan the phosphor screen both horizontally and vertically through the shadow mask, to thereby display a color image.
The shadow mask is for selecting three electron beams emitted from the electron gun to the three-color phosphor layers, and has a substantially rectangular mask main body and a substantially rectangular mask frame fitted to the periphery of the mask main body. The mask main body has a curved effective surface formed with a large number of electron-beam passage apertures and opposing the phosphor screen, a non-aperture portion surrounding the outer periphery of this effective surface, and a skirt portion formed in a bent at almost a right angle with respect to the outer periphery of the non-aperture portion. The mask frame is fitted to the skirt portion of the mask main body. The shadow mask is detachably supported on the panel by engaging wedge-shaped elastic supporting member fixed to the corners of the mask frame with stud pin provided at the corners of the skirt portion of the panel, respectively.
Generally, in order to achieve an image display on the phosphor screen of a color cathode-ray tube without a deviation of color purity, it is necessary to select electron beams so that three electron beams that pass through the electron-beam passage apertures formed on the mask main body of the shadow mask make a correct landing onto the three-color phosphor layers. For this purpose, it is necessary to dispose the shadow mask at a predetermined position with respect to the panel. Particularly, it is necessary to keep the distance (q value) between the inner surface of the effective portion of the panel and the inner surface of the mask main body within a predetermined permissible range of values.
In recent years, a color cathode-ray tube has been desired that the panel is formed in a shape as close to a flat surface as possible by enlarging a radius of curvature of the outer surface of the effective portion of the panel in order to improve visibility. In this case, it is necessary to make larger that radius of curvature of the inner surface of the effective portion, from the viewpoint of the visibility and the strength of the vacuum envelope against the atmospheric pressure. Along with an increase in the radius of curvature of the inner surface of the effective portion, it also becomes necessary to increase the radius of curvature of the effective surface of the mask main body in order to obtain suitable beam landing.
However, the increasing of the radius of curvature of the effective surface of the mask main body lowers the strength for holding the curved surface (hereinafter, referred as a curved surface holding strength) of the shadow mask, and easily causes local deformation of the shadow mask in the process of manufacturing the shadow mask and thermal deformation of the shadow mask in the process of manufacturing a color cathode-ray tube, resulting in a deviation of beam landing which leads to an occurrence of deterioration of color purity. Further, when the color cathode-ray tube is built into a TV set, sound generated from the speaker oscillates the shadow mask, which leads to an easy occurrence of deterioration of color purity.
As a measure for improving the curved surface holding strength of the shadow mask, there has been proposed a technique for providing reinforcing beads on the effective surface of the mask main body in Jpn. Pat. Appln. KOKAI Publication No. 7-161306. However, when reinforcing beads are provided on the effective surface having a large radius of curvature in an attempt to obtain a sufficient curved surface holding strength, stepped portions formed as a result causes a local deviation of the distance between the inner surface of the effective portion of the panel and the effective surface of the mask main body from a permissible range of values for the distance. Accordingly, an image of the stepped portions appear on the screen and this extremely deteriorates the picture quality. To avoid this problem, the limit of the height of the stepped portions formed by the reinforcing beads is usually about 0.1 to 0.2 mm. However, the provision of reinforcing beads of this height on the shadow mask having a large radius of curvature of the effective surface can not sufficiently increase the curved surface holding strength.
The present invention has been contrived in consideration of the above problems, and its object is to provide a color cathode-ray tube which reduces deviation of beam landing and deterioration of color purity by increasing the curved surface holding strength of the shadow mask.
In order to achieve the above object, a color cathode-ray tube according to the present invention comprises: a vacuum envelope including a panel having a substantially rectangular effective portion, a funnel connected to the panel, and a phosphor screen formed on an inner surface of the effective portion of the panel;
a shadow mask disposed to face the phosphor screen within the vacuum envelope, the shadow mask including a substantially rectangular mask main body having a curved effective surface formed with a large number of electron-beam passage apertures and facing the phosphor screen, a non-aperture portion surrounding an outer periphery of the effective surface, and a skirt portion formed in a bent on an outer periphery of the non-aperture portion; and a substantially rectangular mask frame attached to the skirt portion of the mask main body; and
an electron gun arranged within a neck of the funnel, for emitting electron beams to the phosphor screen through the shadow mask.
The mask main body has a long axis extending in a horizontal direction and crossing with a tube axis, and a short axis extending in a vertical direction and crossing with both the tube axis and the long axis, and
the effective surface, or the effective surface and the non-aperture portion of the mask main body are formed in a curved surface having a radius of curvature in the short axis direction, and at each long side of the mask main body, an end portion of the short axis of the effective surface or the non-aperture portion is recessed from any other adjacent part, in a direction to leave from the phosphor screen along the tubular axis.
Further, according to the color cathode-ray tube relating to the present invention, the effective surface, or the effective surface and the non-aperture portion of the mask main body are formed in a curved surface having a radius of curvature in the short axis direction, and at each long side of the mask main body, at least one portion at an intermediate part in the long axis direction of the effective surface or the non-aperture portion is recessed from any other adjacent part, in a direction to leave from the phosphor screen along the tubular axis.
Further, according to the color cathode-ray tube relating to the present invention, the effective surface, or the effective surface and the non-aperture portion of the mask main body are formed in a curved surface having a radius curvature in the short axis direction, and at each long side of the mask main body, at least a part of the effective surface and the non-aperture portion at the vicinity of the short axis is recessed from any other part adjacent in the long axis direction, in a direction to leave from the phosphor screen along the tubular axis.
According to the color cathode-ray tube having the above-described structure, the provision of a recess on each of the long sides of the effective surface or the non-aperture portion of the mask main body makes it possible to maintain high-level strength for holding the curved surface of the effective surface of the mask main body even in the case where the radius of curvature of the effective surface of the mask main body has been increased along an increase in the radius of curvature of the external surface of the effective portion of the panel. Therefore, it is possible to provide a color cathode-ray tube which can minimize an occurrence of deterioration of color purity by restricting local deformation of a shadow mask in the process of manufacturing the shadow mask, thermal deformation of the shadow mask in the process of manufacturing the color cathode-ray tube, or oscillation due to the sound from the speaker when the color cathode-ray tube has been built into a TV set. Particularly, when the present invention is applied to a color cathode-ray tube having an aspect ratio of 16 to 9, the curved-surface holding strength can be increased in good balance over the whole surface of the mask main body. Thus, it is possible to structure a color cathode-ray tube capable of providing satisfactory picture quality by minimizing an occurrence of howling of color purity.
When a recess is provided at the shadow mask, it is very important that the q value does not shift from the permissible range and the image of the recess, which deteriorates the image quality, is not produced on the screen.
Thus, at these portions near the short axis ends (those portions near the long sides), the radius of curvature of the mask main body in the short axis direction has a sufficient value for maintaining the curved surface holding strength, and at the other portion of the mask main body, the radius of curvature is larger than those at the short axis end portions, so that it is possible to delete an influence of the recess at a main region of the effective portion.
Moreover, it is preferable that the radius of curvature of the mask main body at the long axis end portions (short sides) in the short axis direction is larger than the radius of curvature near the short axis so that the shadow mask is seen a substantially flat in order to improve visibility. The radius of curvature of the main body at the long axis end portions in the short axis direction may be more large and may be infinity.
Particularly, in a color cathode-ray tube having an aspect ratio of 16 to 9, since the long sides are longer than normal cathode-ray tubes, it is effective that the radius of curvature of the mask main body in the short axis direction is suitably selected so as to form a recess at each long side (short axis end), and it is more preferable that the short sides are flat.